1. Field of the Invention
The present invention relates to a manufacturing method for a SIMOX substrate for obtaining a SIMOX substrate by subjecting an oxygen-ion-implanted silicon substrate to heat treatment.
This application claims priority from Japanese Patent Application No. 2004-211127 filed on Jul. 20, 2004, the content of which is incorporated herein by reference.
2. Background Art
Known SOI substrates having a single-crystal silicon layer on an insulator such as silicon oxide include SIMOX substrates. SIMOX substrates are SOI substrates where oxygen ions are implanted into a single-crystal silicon substrate and then a high-temperature heat treatment is carried out in an oxidizing atmosphere to cause chemical reactions between the implanted oxygen ions and silicon atoms so that a buried oxide film is formed. Because devices formed on these SOI layers achieve high radioresistance, latch-up resistance, control of a short channel effect, and low-power-consumption operation, SOI substrates are expected as next-generation high-performance semiconductor substrates.
In general, for mirror-polished substrates produced by processing a silicon single crystal grown by the Czochralski method, crystal defects, such as COPs (Crystal Originated Particles), introduced during silicon growth are known to contribute to degradation in the resistance characteristic of a gate oxide film. For this reason, device manufacturers provide an improvement in yield due to poor insulation of a gate oxide film by using substrates with low crystal defect density, such as silicon epitaxial growth substrates or substrates with significantly reduced crystal defects that are grown at a low pull rate.
The same also applies to SOI substrates, and similarly for SIMOX substrates, any COPs or void defects existing on or near the substrate surface bring about, for example, a pinhole defect on a SOI layer surface of the finished product, thus degrading device characteristics. A manufacturing method for a SIMOX substrate is proposed which is free of pinhole defects on this SOI layer surface by using a silicon single crystal which includes 1×1014 atoms/cm3 to 1×1017 atoms/cm3 of nitrogen (refer to, for example, Japanese Unexamined Patent Application, First Publication No. H10-64837). In this manufacturing method for a SIMOX substrate where oxygen ions were implanted into a silicon substrate including nitrogen, heat treatment was performed at 1350° C. in 0.5% oxygen gas for four hours, and heat treatment was continued for another four hours at an oxygen concentration of 70%, it is reported that there were no pits (called thermal pits) measuring greater than or equal to 0.3 μm in size on a SOI layer surface.
It is true that there were substantially no thermal pits measuring greater than or equal to 0.3 μm in size on the SOI layer surface of the silicon substrate including nitrogen into which oxygen ions were implanted and which were then subjected to heat treatment. However, it has been found that defects smaller than 0.3 μm in size existed at high density near the surface. In other words, this phenomenon indicates that crystal defects are not eliminated in an atmosphere including a very low concentration of oxygen, and therefore, the above-described known manufacturing method has a problem in that defects of smaller than 0.3 μm in size cannot be eliminated.